The invention relates to procedures and apparatus for ophthalmic surgery upon the cornea to correct one or more optical deficiencies of an eye. More particularly, the invention is concerned with controlled use of tissue-ablating laser-beam irradiation of stromal tissue within the optically used central area of the cornea, to effect improved optical performance at the anterior surface of the cornea. And the invention is specifically concerned with the class of surgical procedures which includes keratomileusis and thus a temporary partial or total surgical removal of the lenticle from the cornea.
Origin of keratomileusis and related procedures is attributed to Dr. Jose I. Barraquer, of Bogota, Colombia. His procedures and apparatus are described and illustrated by Dr. Louis J. Girard, in his 1981 authoritative text, "Corneal Surgery", Volume Two, Chapter 6 ("Refractive Keratoplasty"), pp. 143 to 172; Dr. Girard's Chapter 6 concludes with a full bibliography which accounts for the contributions of Dr. Barraquer and others in the art.
It suffices for present purposes to briefly describe Dr. Barraquer's keratomileusis procedure, which is visually employed for surgically correcting a severely myopic eye, although it can also be used to correct for a hyperopia condition. At the outset, a special microtome (a "microkeratome") is applied to the cornea and operates to shear off, as a lenticle, namely, a central front truncation of predetermined size, from the central region of the cornea, the diameter of the truncation being in the order of 7.5 mm and thus fully embracing the optically used region of the cornea. Having selected a holding disc for its concavity adapted to the front-surface curvature of the lenticle, the lenticle is fitted to the concavity, and is then frozen, with the freshly cut posterior surface of the lenticle exposed for precision lathing to predetermined contour. After lathing and thawing, the lenticle is reapplied to the eye, and is then sutured in stroma-to-stroma contact with the cornea from which it was removed.
A keratomileusis procedure thus contemplates full preservation of the anterior surface of the cornea, and a lathe-sculpturing removal of stromal tissue only from the posterior surface of the severed lenticle. If the lathing is to a characterized predetermined depth of cut which is greatest at the optical axis and which reduces to zero at the outer radius of the optically used part of the cornea, then upon applying the lathed lenticle to the eye, a myopia-correcting result is obtained. If, on the other hand, the lathing depth of cut is greatest at the outer radius of the optically used part of the cornea, with reducing depth of cut as a function of reducing radius, then a hyperopia-correcting result is obtained.
We know of no reported efforts to apply laser surgery in any updated performance of a keratomileusis operation. However, Trokel, et al. in their paper entitled "Excimer Laser Surgery of the Cornea", Am. J. Ophthal. 96: 710-715, December 1983, do suggest the possibility of such an operation.
Meanwhile, various L'Esperance, Jr. patents have issued, describing use of tissue-ablating laser radiation, directed to the optically used central region of the anterior surface of the cornea, to effect optical correction by tissue-ablating action, with volumetric removal of corneal tissue. These patents illustratively include those numbered 4,665,913, 4,669,466, 4,732,148, 4,729,372, and 4,770,172, and their disclosures, as well as Dr. Girard's said Chapter 6, are hereby incorporated by reference.